Each year worldwide several millions of patients undergo cardiac bypass surgery, during which stenosed and atherosclerotic cardiac vessels are replaced with native veins or arteries harvested elsewhere from the body.
A first step in treating or correcting cardiac disease, such as coronary artery disease, is to determine which portions of the heart are most likely to benefit from revascularization. In this manner, the clinician is able to assess the functioning of the myocardium, the location of infarcted or distressed areas, and select an appropriate treatment plan, e.g., an open-chest surgical procedure, “keyhole” coronary artery bypass grafting (“CABG”) or angioplasty. Several methods of determining cardiac functioning are described, for example, in Udelson, “Steps Forward in the Assessment of Myocardial Viability in Left Ventricular Dysfunction,” Circulation, 97:833–838 (1998). It would therefore be desirable to provide methods and apparatus that enhance a clinician's ability to better assess left ventricular dysfunction.
Patients often experience irreversible damage to ischemic myocardium while awaiting corrective therapy or surgery. It would therefore be desirable to provide apparatus and methods for preserving the myocardium of patients awaiting a corrective procedure.
A number of techniques have been developed to preserve the myocardium during corrective procedures, such as angioplasty and bypass procedures, that involve perfusing the heart using the coronary venous system. For cardiac surgery, a patient's heart is typically stopped, and the patient is placed on a cardiopulmonary bypass machine. Hypothermia is induced and maintained in the heart throughout the bypass operation to reduce necrosis of the myocardium caused by oxygen starvation.
Coronary retroperfusion also may be used to preserve ischemic myocardium, as described in Kuraoka et al., “Antegrade or Retrograde Blood Cardioplegic Method: Comparison of Post-Surgical Right Ventricular Function and Conduction Disturbances,” Japanese J. Thoracic Surg., 48(5):383–386 (1995); Ihnken et al., in “Simultaneous Arterial and Coronary Sinus Cardioplegic Perfusion, an Experimental and Clinical Study,” Thoracic and Cardiovascular Surgeon, 42(6):141–147 (1994); and Lincoff et al., “Percutaneous Support Devices for High Risk or Complicated Coronary Angioplasty,” J. Am. Coll. Cardiol., 17(3):770–780 (1991)).
Retrograde blood flow through the coronary venous system may be augmented by coronary ostial occlusion, as described in Rudis et al. in “Coronary Sinus Ostial Occlusion During Retrograde Delivery of Cardioplegic Solution Significantly Improves Cardioplegic Distribution and Efficiency,” J. Thoracic &Cardiovasc. Surg., 109(5):941–946 (1995). In this case, blood flows retrograde to the myocardium and drainage is through the lymphatic system and the Thebesian veins.
Aldea, et al., in “Salvage of Ischemic Myocardium With Simplified and Even Delayed Coronary Sinus Retroperfusion,” Ann. Thorac. Sure., 62:9–15 (1996), describe three techniques for preserving ischemic myocardium during a simulated bypass operation. The first method, referred to as pressure-controlled intermittent coronary sinus retroperfusion (“PICSO”) involves placing a balloon in the coronary sinus, which is periodically inflated and deflated. When the balloon is inflated, blood draining into the coronary sinus is passively redirected in a retrograde manner through the coronary venous system, thereby perfusing the myocardium.
A second method described in the Aldea article is synchronized retroperfusion (“SRP”). In SRP, a balloon is placed in the coronary sinus, and in synchrony with balloon inflation, oxygenated blood is pumped into the coronary sinus so that it flows in a retrograde manner. The balloon is inflated, and blood injected into the coronary sinus, only during diastole. During systole, the balloon is deflated and blood flow into the coronary sinus ceases.
A third method, described in the Aldea article as simplified retroperfusion (“SR”), is similar to SRP, but no balloon is placed in the coronary sinus. Instead, a pump is used to continuously inject blood into the coronary sinus. Apparatus suitable for use with the foregoing methods is described in U.S. Pat. No. 5,597,377 to Aldea.
The foregoing methods generally may be used as adjuncts to hypothermia to preserve the myocardium during stenting or high-risk percutaneous transluminal coronary angioplasty (PTCA). Surgical techniques, however, such as developed by Cardio Thoracic Systems, of Menlo Park, Calif., also enable coronary artery bypass grafting (“CABG”) to be performed on a beating heart. In accordance with those methods, the heart is not stopped, but instead the bypass surgery is performed while the heart is beating. It therefore would be desirable to provide simpler methods and apparatus that enable the clinician to preserve the myocardium during beating heart cardiac surgery, PTCA or stenting.
In addition, once the bypass operation is completed, the heart is revived and blood flow through the heart is restored to normal. In some cases, however, there may be some difficulty in weaning the patient from the cardiopulmonary bypass machine. In particular, the heart can become overexerted when attempting to restore flow in the arterial system. In these situations, an intra aortic balloon pump (“IABP”) may be used to lower the pressure encountered by the left ventricle during systole.
The intra-aortic balloon pump generally comprises a balloon catheter which is placed in the ascending aorta or aortic arch, and which is cyclically inflated and deflated in synchrony with the heart. In particular, the balloon is inflated during cardiac diastole, so that blood in the aorta is urged into the descending aorta. The balloon is then deflated in anticipation of systole, and reduces the pressure against which the left ventricle ejects blood during contraction.
In “Enhanced Preservation of Acutely Ischemic Myocardium With Transseptal Left Ventricular Assist,” Ann. Thor. Sure. 57:570–575 (1994), Fonger et al., describe an experimental left ventricular assist device (“LVAD”) for use in weaning a cardiac bypass patient from a cardiopulmonary bypass machine. The device comprises a pump having an inlet catheter disposed in the left atrium via a femoral vein and an outlet catheter located in a femoral artery. The article describes that the LVAD device reduces the load on the left ventricle by draining a portion of the blood from the left atrium into the femoral artery.
It also would be desirable to provide apparatus and methods that assist the left ventricle, by reducing the volume of blood pumped by, and thus, the exertion of, the left ventricle in patients awaiting, or who have completed, cardiac bypass surgery.